Satellite radio links can be used to transmit data in areas of coverage that are a long way from the conventional infrastructure. Satellite radio links are also used for data transmission lines that are only required in the short term, for example for radio broadcast reporting. In most instances, as with GSM mobile radio, individual users are provided by the operator of the satellite with so-called SIM cards, which are used to identify and charge users.
The user can use a satellite modem with corresponding SIM card and connected transmit apparatus to utilize various services of the satellite radio link and/or the infrastructure connected downstream of this and thus for example accept a data connection to the internet or exchange data directly with a further user. To this end the user can request a so-called allocated or dedicated channel, which has certain characteristics (e.g. bandwidth) guaranteed by the operator of the satellite. It is also possible to utilize a general channel (background channel), which is available to all users at the same time and therefore certain transmission characteristics of this general channel are not guaranteed for individual users. However in practice it is desirable to use this general channel by preference, as this allows much more economical data transmission than when an allocated channel is used, in particular as time-dependent charges are generally incurred for reserving an allocated channel, while billing is based on data quantities when the general channel is used.
U.S. Pat. No. 5,826,190A describes a method which allows switching between satellite radio channels if a subscriber terminal experiences receive problems on the channel allocated to it. U.S. Pat. No. 5,561,838A discloses a similar method, in which data transmission is switched to a channel of a further satellite and the parameters required for this are determined and transferred.